1. Field of the Invention
The present invention relates to new liquid crystalline compounds as well as liquid crystalline compositions containing at least one of the liquid crystalline compounds. More particularly, the present invention relates to ferroelectric liquid crystals and to new p-terphenyl derivatives which are useful as components for preparing practical ferroelectric liquid crystalline compositions and excellent in chemical stability as well as liquid crystalline compositions containing at least one of the p-terphenyl derivatives.
2. Description of the Prior Art
Liquid crystal display elements are widely used as display elements in watches, electronic desk-top computers, personal word processors, pocket-size TV sets, etc. They possess such beneficial characteristics as no eyestrain, because of their passive device, low electric power consumption, thin structure, etc. However, they are restricted in their practical applications because of slow response time and lack of memory effect. In an attempt to expand their areas of application there have been provided, for example, the super twisted nematic (STN) display system, which is an improvement of the twisted nematic (TN) display system. These systems, however, are not sufficient for large screen or graphic display use. Various studies have therefore been made of liquid crystal display elements which can supersede them. One such display system [N. A. Clark et al., Applied Phys. lett., 36, 899 (1980)] utilizes ferroelectric liquid crystals [R. B. Meyer et al., Physique, 36 L-69 (1975)]. Because of its advantageous characteristics such as fast response, which is 100 times conventional systems, and memory effect, it is expected to expand areas of application of liquid crystal display elements. The term "ferroelectric liquid crystal" is used to mean a series of smectic liquid crystals whose molecular longitudinal axis is at a certain angle to the normal of the layer, but in practice the chiral smectic C (SmC*) phase is utilized.
In practice, ferroelectric liquid crystals for display elements are used as a liquid crystalline composition comprising a number of ferroelectric liquid crystalline compounds or prepared by blending such compound(s) and one or more compounds having the smectic C (SmC) phase. As is the case with the preparation of nematic liquid crystal display elements, mixing a number of components is required if different properties needed for actual use, such as operating temperature range, response time, helical pitch, chemical stability and so on, are to be achieved.
Ferroelectric liquid crystalline compositions have not been put to actual use as of yet. In particular, there has been a need for the development of substances which show the SmC phase over a wide temperature range, and which have the SmC* phase and an adequate spontaneous polarization value. The object of the present invention is to provide new substances which satisfy such a need.
Known p-terphenyl compounds of analogous structure are disclosed, for example, in EP-013277, GB-2200912 and Mol. Cryst. Liq. Cryst., 1985, Vol. 123, pp. 185-204.
The present invention provides substances which have a wider temperature range for the SmC or SmC* phase than these known compounds, as well as substances which have SmC* phase and an adequate spontaneous polarization value.